Currently, colored digital images are derived through various means including digital cameras and the digital scanning of film images. Many times the sharpness of a colored digital image is degraded by optical elements or by irregularities in the image sensor. For these reasons, it is often desirable to sharpen the color image after it has been converted to a digital representation. However, these digital images also tend to be noisy. For example, one noise source is sensor noise in both digital cameras and film scanners.
The problem with sharpening a noisy image is well known. Noise manifests itself as erroneous image fluctuations which are usually difficult to distinguish from the subtle image features which need sharpening. Thus, conventional sharpening processes amplify noise as well as image content. What is needed is a process that can sharpen image detail without further accentuating any noise present in the image.
Another consideration is that interpolated color images from digital cameras may have differences in edge sharpness depending on edge orientation and the details of the color interpolation algorithm. As a result, different regions of a colored digital image may require different levels of sharpening depending on edge orientation.